U.S. patent number 7,685,839 [Application Number 11/177,855] was granted by the patent office on 2010-03-30 for refrigeration system.
Invention is credited to Junjie Gu.
United States Patent |
7,685,839 |
Gu |
March 30, 2010 |
Refrigeration system
Abstract
A refrigeration system with integrated accumulator-expander-heat
exchanger is disclosed. Refrigerant from a condenser/gas cooler is
throttled through a capillary tube while at the same time
undergoing a heat exchanging process with refrigerant from an
evaporator. This method can elevate the compressor efficiency,
increase the specific cooling capacity, and enhance the system
performance. The capillary tube, which has dual functions of
expansion device and heat exchanger, is placed inside a canister
which also functions as an accumulator. The new device combining
three separate parts into one can simplify the manufacturing
process, lower the system size and weight, and thus decrease cost
of the whole system.
Inventors: |
Gu; Junjie (Ottawa, Ontario,
CA) |
Family
ID: |
35783470 |
Appl.
No.: |
11/177,855 |
Filed: |
July 8, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060010905 A1 |
Jan 19, 2006 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60586297 |
Jul 9, 2004 |
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Current U.S.
Class: |
62/503; 62/434;
62/197 |
Current CPC
Class: |
F25B
41/37 (20210101); F28D 7/024 (20130101); F25B
40/00 (20130101); F25B 41/39 (20210101); F25B
43/006 (20130101); F28D 7/14 (20130101); F25B
2400/052 (20130101); F25B 2400/051 (20130101); F25B
2309/061 (20130101); F25B 9/008 (20130101) |
Current International
Class: |
F25B
43/00 (20060101) |
Field of
Search: |
;62/503,511,513,197,113,434 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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210 267 |
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Jun 1940 |
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CH |
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14 51 039 |
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Mar 1969 |
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DE |
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2 528 157 |
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Dec 1983 |
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FR |
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2 836 542 |
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Aug 2003 |
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FR |
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16179 |
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Jul 1914 |
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GB |
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58 016153 |
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Jan 1983 |
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JP |
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11 002474 |
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Jan 1999 |
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JP |
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2002 267278 |
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Sep 2002 |
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JP |
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2004-028525 |
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Jan 2004 |
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JP |
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2004 028525 |
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Jan 2004 |
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JP |
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Other References
Supplementary Partial European Search Report for European
Application No. EP05 76 3488 (4 pages), Search completed Jun. 1,
2007. cited by other.
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Primary Examiner: Jones; Melvin
Attorney, Agent or Firm: Barnes & Thornburg LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority from U.S. Provisional Patent
Application No. 60/586,297 filed on 9 Jul, 2004.
Claims
The invention claimed is:
1. An apparatus for a refrigeration system comprising an
accumulator having a chamber for receiving refrigerant; an expander
for expanding refrigerant and disposed in said chamber, wherein
said expander comprises a conduit for carrying refrigerant
therethrough, said conduit having an impedance over at least a
portion of its length to produce a pressure drop in fluid
therealong; an enclosure in said chamber for carrying gaseous
and/or two-phase refrigerant therealong, said enclosure being
defined by an enclosure wall and having a fluid inlet, a fluid
outlet, and a portion disposed in a lower portion of said
accumulator, the lower portion of the enclosure having one or more
bleed holes formed therein for introducing fluid from said chamber
into said enclosure, and wherein a major surface area of said
conduit is in heat exchange relationship with the interior of said
enclosure.
2. An apparatus as claimed in claim 1, wherein said expander
conduit is disposed in said enclosure.
3. An apparatus as claimed in claim 1, wherein said enclosure
comprises a conduit.
4. An apparatus for a refrigeration system, comprising an
accumulator having a chamber for receiving refrigerant; an
enclosure in said chamber, said enclosure being defined by an
enclosure wall and having a fluid inlet and a fluid outlet, said
accumulator chamber having upper and lower portions, said enclosure
extending between said upper and lower portions of the accumulator
chamber, and having a lower portion disposed in the lower portion
of said chamber, an aperture being formed in the lower portion of
said enclosure for introducing fluid from the interior of said
chamber into said enclosure; an expander for expanding refrigerant
and disposed in said enclosure, wherein said expander comprises a
conduit for carrying refrigerant therethrough, said conduit having
an impedance over at least a portion of its length to produce a
pressure drop in fluid therealong; and separating means for
separating refrigerant gas from refrigerant liquid and for
introducing refrigerant gas into the inlet of said enclosure,
wherein said separating means comprises a fluid inlet for
introducing fluid into said chamber and which is positioned to
prevent fluid flowing through said inlet into said chamber from
flowing directly into the inlet of said enclosure.
5. An apparatus for a refrigeration system, comprising an
accumulator having a chamber for receiving refrigerant; an
enclosure in said chamber, said enclosure being defined by an
enclosure wall and having a fluid inlet and a fluid outlet, said
accumulator chamber having upper and lower portions, said enclosure
extending between said upper and lower portions of the accumulator
chamber, and having a lower portion disposed in the lower portion
of said chamber, an aperture being formed in the lower portion of
said enclosure for introducing fluid from the interior of said
chamber into said enclosure; an expander for expanding refrigerant
and disposed in said enclosure, wherein said expander comprises a
conduit for carrying refrigerant therethrough, said conduit having
an impedance over at least a portion of its length to produce a
pressure drop in fluid therealong; and an expansion device defining
one or more restrictive orifices sized to increase the impedance of
fluid flow above the impedance provided by said expander
conduit.
6. An apparatus as claimed in claim 5, further comprising valve
means for varying the size of at least one orifice.
7. An apparatus for a refrigeration system, comprising an
accumulator having a chamber for receiving refrigerant; an
enclosure in said chamber, said enclosure being defined by an
enclosure wall and having a fluid inlet and a fluid outlet, said
accumulator chamber having upper and lower portions, said enclosure
extending between said upper and lower portions of the accumulator
chamber, and having a lower portion disposed in the lower portion
of said chamber, an aperture being formed in the lower portion of
said enclosure for introducing fluid from the interior of said
chamber into said enclosure; an expander for expanding refrigerant
and disposed in said enclosure, wherein said expander comprises a
conduit for carrying refrigerant therethrough, said conduit having
an impedance over at least a portion of its length to produce a
pressure drop in fluid therealong; and a further conduit for
carrying fluid from said accumulator to a compressor and a return
conduit for feeding fluid from said compressor to said accumulator
and wherein said further and return conduits are in heat exchange
relationship.
8. An apparatus as claimed in claim 7, wherein at least one of (1)
the walls of the further and return conduits are in contact with
one another and (2) one of said further conduit and said return
conduit is inside the other of said further conduit and said return
conduit.
9. An apparatus for a refrigeration system, comprising an
accumulator having a chamber for receiving refrigerant; an
enclosure in said chamber, said enclosure being defined by an
enclosure wall and having a fluid inlet and a fluid outlet, said
accumulator chamber having upper and lower portions, said enclosure
extending between said upper and lower portions of the accumulator
chamber, and having a lower portion disposed in the lower portion
of said chamber, an aperture being formed in the lower portion of
said enclosure for introducing fluid from the interior of said
chamber into said enclosure; an expander for expanding refrigerant
and disposed in said enclosure, wherein said expander comprises a
conduit for carrying refrigerant therethrough, said conduit having
an impedance over at least a portion of its length to produce a
pressure drop in fluid therealong; wherein said conduit has an
impedance which is distributed over a substantial portion of its
length in said chamber.
10. An apparatus for a refrigeration system comprising an
accumulator having a chamber for receiving refrigerant, and
expansion means for expanding refrigerant, the expansion means
comprising a conduit for carrying fluid therethrough and being
arranged for exchanging heat with refrigerant in said chamber, said
conduit having an impedance over at least a portion of its length
to produce a pressure drop in fluid therealong, said expansion
means further comprising means for defining one or more restrictive
orifice sized to increase the impedance of fluid flow above the
impedance provided by said conduit, and valve means, responsive to
a parameter to vary the size of at least one orifice.
11. An apparatus as claimed in claim 10, wherein said parameter
comprises at least one of temperature and pressure.
12. An apparatus as claimed in claim 10, wherein said valve means
comprises structure which displaces as a result of changes in
temperature of the structure.
13. An apparatus as claimed in claim 12, wherein said structure
comprises an element capable of assuming a curve along its length
and wherein the tightness of an assumed curve is varied by
temperature such that the tightness of curvature is varied in a
plane which extends across said orifice.
14. An apparatus as claimed in claim 13, wherein said element
comprises a first element comprising a first material and a second
element comprising a second material wherein the first material has
a different coefficient of thermal expansion than that of said
second material and said elements are positioned side by side in
said plane.
15. An apparatus as claimed in claim 14, wherein said element
comprises an elongate strip formed as a spiral.
16. An apparatus as claimed in claim 15, wherein said element is
mounted such that said element overlaps said orifice to vary the
size of said orifice.
17. An apparatus for a refrigeration system comprising an
accumulator having a chamber for receiving refrigerant, an expander
for expanding refrigerant comprising a conduit for carrying fluid
therethrough, said conduit having an impedance over at least a
portion of its length to produce a pressure drop in fluid
therealong, and a controller responsive to a parameter to control
the impedance of the expander, wherein said controller comprises
valve means for controlling the flow of fluid therethrough.
18. An apparatus as claimed in claim 17, wherein said conduit is
disposed within said chamber.
19. An apparatus as claimed in claim 18, further comprising an
enclosure being defined by an enclosure wall and having a fluid
inlet and a fluid outlet, and wherein the expander conduit is
disposed in said enclosure.
20. An apparatus as claimed in claim 17, wherein said expander
conduit has an inlet and an outlet, and wherein said valve means is
positioned proximate the outlet.
21. An expansion device for a refrigeration system, the expansion
device having one or more restrictive orifices, a valve element for
varying the size of at least one orifice, wherein the valve element
is capable of assuming a curve along its length, the assumed curve
having a tightness, and wherein the tightness of the assumed curve
of said element is varied by temperature such that the tightness of
the assumed curve is varied in a plane which extends across the
orifice.
22. An expansion device as claimed in claim 21, comprising a
transverse member, said one or more restrictive orifices being
formed in said transverse member, and wherein said valve element is
positioned against said transverse member.
23. An expansion device as claimed in claim 21, wherein said valve
element comprises a first element comprising a first material and a
second element comprising a second material, wherein said first
material has a different coefficient of expansion than that of the
second material, and said elements are positioned side by side in
said plane.
24. An expansion device as claimed in claim 23, wherein said valve
element comprises an elongate strip formed as a spiral.
25. An expansion device as claimed in claim 22, wherein said one or
more restrictive orifices each has a high pressure side and a low
pressure side, and said valve element is positioned on the high
pressure side.
26. An apparatus for a refrigeration system, comprising an
accumulator having a chamber for receiving refrigerant; an
enclosure in said chamber, said enclosure being defined by an
enclosure wall and having a fluid inlet and a fluid outlet, said
accumulator chamber having upper and lower portions, said enclosure
extending between said upper and lower portions of the accumulator
chamber, and having a lower portion disposed in the lower portion
of said chamber, an aperture being formed in the lower portion of
said enclosure for introducing fluid from the interior of said
chamber into said enclosure; an expander for expanding refrigerant
and disposed in said enclosure, wherein said expander comprises a
conduit for carrying refrigerant therethrough, said conduit having
an impedance over at least a portion of its length to produce a
pressure drop in fluid therealong; wherein said enclosure comprises
a first portion defining a downwardly directed flow passage for
refrigerant between said upper portion of said accumulator chamber
and said lower portion of said enclosure, and a second portion
defining an upwardly directed flow passage for said refrigerant
from said lower portion of said enclosure towards said upper
portion of said accumulator chamber.
27. An apparatus for a refrigeration system, comprising an
accumulator having a chamber for receiving refrigerant; an
enclosure in said chamber, said enclosure being defined by an
enclosure wall and having a fluid inlet and a fluid outlet, said
accumulator chamber having upper and lower portions, said enclosure
extending between said upper and lower portions of the accumulator
chamber, and having a lower portion disposed in the lower portion
of said chamber, an aperture being formed in the lower portion of
said enclosure for introducing fluid from the interior of said
chamber into said enclosure; an expander for expanding refrigerant
and disposed in said enclosure, wherein said expander comprises a
conduit for carrying refrigerant therethrough, said conduit having
an impedance over at least a portion of its length to produce a
pressure drop in fluid therealong; wherein said enclosure comprises
a conduit, and said enclosure conduit includes a first arm defining
a downwardly directed flow path for refrigerant between said upper
portion of said accumulator chamber and said lower portion of said
enclosure, and a second arm defining an upwardly directed flow path
for said refrigerant from said lower portion of said enclosure
towards said upper portion of said accumulator.
28. An apparatus as claimed in claim 1, wherein said expander
conduit comprises a capillary tube.
29. An apparatus, as claimed in claim 1, wherein said expander
conduit is non-linear along at least a portion of its length in
said enclosure.
30. An apparatus as claimed in claim 29, wherein said expander
conduit defines a spiral or a meander shape along at least a
portion of its length in said enclosure.
Description
FIELD OF THE INVENTION
The present invention relates generally to refrigeration systems
with a heat exchanger, and more particularly but not limited to
transcritical systems used in automobile vehicles, e.g. in the form
of CO.sub.2 air conditioners.
BACKGROUND OF THE INVENTION
Closed-loop refrigeration/heat pump systems conventionally employ a
compressor that is meant to draw in vaporous refrigerant at
relatively low pressure and discharges hot refrigerant at
relatively high pressure. The hot refrigerant is then cooled in a
gas cooler if the pressure and temperature are higher than values
of temperature and pressure at the critical point, otherwise it
condenses into liquid, and the gas cooler is called a condensers,
accordingly. "Critical point" is a physical property of pure
substances defined by temperature and pressure. Above the critical
point, the substance is in a supercritical state and comprises a
supercritical fluid which is neither gas nor liquid.
Together with a compressor, an expansion device, which typically
comprises an expansion valve, or in some cases may comprise one or
plurality of capillary tube(s), divides the system into high and
low pressure sides. The working fluid passes through the expansion
device into an evaporator, and as it passes through the expansion
device the fluid expands and cools. The fluid typically enters the
evaporator in a liquid-rich state, and thereafter absorbs heat and
evaporates. At low heat loads in certain working conditions it is
not possible to evaporate all the liquid. Some amount of liquid
refrigerant is used to dilute cycling oil and carry it back to the
compressor. However, a large amount of liquid is undesirable
because system efficiency could be lowered and the compressor could
be significantly damaged if a large amount of liquid refrigerant
enters the compressor (known as "liquid slugging"). Therefore, it
is preferable to place an accumulator between the evaporator and
the compressor to separate vapour and liquid and store the excess
liquid. Accumulators have a metering function of collecting liquid
and returning a certain amount to the compressor. This prevents
liquid slugging and controls oil return. It is particularly
important in automobile air conditioning systems, where surges of
liquid refrigerant occur frequently because of the varying dynamic
operating conditions. Moreover, use of an accumulator can elevate
the efficiency of the evaporator in that dry coils, employed in
traditionally operated evaporators, are not required.
Transcritical refrigerating systems operate in a range of
temperature and pressure that cross the critical point of the
refrigerant. In these systems, for refrigerants with relatively low
critical temperatures, e.g. carbon dioxide which has a critical
temperature of 31.7.degree. C., it is difficult to reach a high
specific cooling capacity and this is a significant barrier for
achieving a high coefficient of performance (COP). To overcome this
limitation, an internal heat exchanger is used that exchanges heat
between refrigerants of different parts; one which connects the
condenser/gas cooler and expansion device, and the other which
connects the evaporator and compressor. This method is described in
U.S. Pat. No. 5,245,833, 6,523,365 and 6,681,597.
Another feature of a known refrigeration system is the inclusion of
the expander in the accumulator-heat exchanger system (U.S. Pat.
Nos. 5,622,055 and 6,530,230). However, in U.S. Pat. No. 6,530,230,
an expansion device is simply assembled at the inlet of
accumulator-heat exchanger without being functionally
integrated.
In U.S. Pat. No. 5,622,055, an expander, a heat exchanger, and an
accumulator are integrated into a canister. However, those
explorations focus only on subcritical refrigerants. The
characteristics of trans-/hypercritical alternatives were not
considered; accordingly, a phase change from supercritical fluid to
liquid which occurs in trans-hypocritical systems was not taken
into account in the expander design. Additionally, the capillary
coils were required to be immersed in the liquid-phase of the
accumulator. This will not increase the specific cooling capacity,
and the extra circulating refrigerant needed will consume more
energy. As a result, the whole system performance might not be
improved significantly. Furthermore, the heat gain from environment
between the evaporator outlet and the inlet of compressor
(including accumulator) will decrease the system COP.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided
an apparatus for a refrigeration system comprising an accumulator
having a chamber for receiving refrigerant, an enclosure in said
chamber, said enclosure being defined by an enclosure wall and
having a fluid inlet and a fluid outlet, and an expander for
expanding refrigerant and disposed in said enclosure, wherein said
expander comprises a conduit for carrying refrigerant therethrough,
said conduit having an impedance over at least a portion of its
length to produce a pressure drop in fluid therealong.
In this arrangement, the expansion device comprises a conduit whose
wall provides a heat exchange surface so that, for example,
refrigerant flowing through the expansion conduit to an evaporator
of the refrigeration system can exchange heat with refrigerant
flowing from the evaporator to a compressor. Positioning the
expansion conduit within an enclosure in the accumulator chamber at
least partially isolates the expansion conduit from liquid
refrigerant in the accumulator chamber and allows refrigerant
flowing through the conduit to exchange heat predominantly with
gaseous and/or two-phase refrigerant received from the evaporator
of the refrigeration system. This arrangement both obviates the
need for a separate expansion device, thereby allowing the
refrigeration system to be more compact, and promotes a heat
exchange process which assists in preventing liquid refrigerant
flowing into the compressor. This arrangement also reduces the
evaporation of liquid refrigerant in the accumulator so that more
liquid is available in the evaporator, thereby increasing the
efficiency and cooling capacity of the refrigeration system. As the
system does not depend on any heat exchange with liquid refrigerant
in the accumulator, the present arrangement is particularly
suitable for use with transcritical refrigerants such as CO.sub.2
in which liquefaction of the refrigerant is more difficult than
other more conventional refrigerants.
In some embodiments, the conduit has an impedance which is
distributed over a substantial portion of its length in the
enclosure and in one embodiment may comprise a capillary tube.
Generally, the expansion conduit provides a sufficient impedance to
produce a sufficient pressure drop in fluid flowing therethrough
for introduction into an evaporator.
In some embodiments, the apparatus further comprises separating
means for separating refrigerant gas from refrigerant liquid and
for introducing refrigerant gas into the inlet of the enclosure.
The separating means may comprise a fluid inlet for introducing
fluid into the chamber, and which is positioned to prevent fluid
flowing through the inlet from flowing directly into the inlet of
the enclosure. Thus, liquid can accumulate in a lower portion of
the chamber, and gaseous refrigerant may be drawn into the
enclosure inlet from the space above the liquid.
In some embodiments, the enclosure is in the form of a conduit and
the expansion conduit extends along the length of the enclosure
conduit so that gaseous and/or two phase refrigerant from the
chamber flows over the surface of the conduit to promote heat
exchange with high pressure refrigerant flowing through the
expansion conduit.
In some embodiments, the apparatus may further comprise an
expansion device defining one or more restrictive orifices sized to
increase the impedance of fluid flow above the impedance provided
by the expander conduit. Advantageously, the addition of an
orifice-type expansion device which contributes to the overall
impedance of the combination allows the impedance of the expander
conduit to be relaxed or reduced. In turn, this allows the
cross-sectional area, and therefore the surface area of the
expander conduit to be increased for improved heat exchange with
refrigerant flowing from the evaporator to a compressor of a
refrigeration system. Alternatively, or in addition, this
arrangement allows the length of the expansion conduit to be
reduced, thereby enabling the expansion conduit to be more
compact.
In some embodiments, the apparatus further comprises valve means
for varying the size of at least one orifice of the expansion
device. Advantageously, this allows the impedance of the
combination expander and therefore the temperature of the
refrigerant at the inlet of the evaporator to be controlled.
Therefore, the valve means allows the cooling capacity of a
refrigeration system to be controlled independently of compressor
speed. This is particularly beneficial in automotive air
conditioning systems where the compressor is driven by the engine
and therefore the compressor speed depends on the speed of the
vehicle. For example, the compressor speed will be low when the
vehicle is idling but the heat load on the system may remain
constant. In this case, the reduction in cooling capacity resulting
from a lower compressor speed can be compensated by controlling the
valve means to increase the pressure drop across the combination
expander, thereby reducing the temperature of refrigerant at the
inlet of the evaporator and increasing the cooling capacity of the
system.
In some embodiments, the valve means is responsive to a parameter
such as temperature or pressure to vary the size of the orifice.
The valve means may comprise structure which displaces as a result
of changes in temperature of the structure. Advantageously, this
allows the valve means to automatically open and close in response
to local temperature changes, such as temperature changes at the
inlet of the evaporator.
In some embodiments, the structure comprises an element capable of
assuming a curve along its length, and wherein a tightness of an
assumed curve is varied by temperature such that the tightness of
curvature is varied in a plane which extends across the orifice.
Advantageously, this arrangement provides a compact and robust
means of operating the orifice valve.
In some embodiments, the element comprises a first element
comprising a first material and a second element comprising a
second material, wherein the first material has a different
coefficient of thermal expansion than that of the second material,
and the elements are positioned side by side in the plane. In some
embodiments, the element comprises an elongate strip formed as a
spiral.
In some embodiments, the apparatus further comprises a conduit for
carrying fluid from the accumulator to a compressor and a return
conduit for feeding fluid from the compressor to the accumulator,
and wherein the further and return conduits are in heat exchange
relationship. This arrangement allows additional heat exchange
between fluid flowing to the compressor and fluid flowing from the
compressor in the portion of the refrigeration circuit between the
accumulator and compressor (e.g. between a cooler/condenser of the
system and the accumulator) to improve the efficiency of the
system. The further and return conduits may be in contact with one
another and/or one conduit may be inside the other to effect heat
exchange between fluids flowing therethrough. In some embodiments,
the return conduit may provide an impedance along at least a
portion of its length, and may, for example, comprise a capillary
tube, and may simply be an extension of the expander conduit in the
accumulator chamber. In another embodiment, an accumulator may be
omitted altogether and the arrangement may simply comprise two
conduits in heat exchange relationship, one of which carries fluid
to the evaporator, and the other carries fluid from the evaporator
to the compressor. In one embodiment, at least a portion of the
conduit carrying fluid to the evaporator may comprise an expansion
conduit, i.e. a conduit which performs expansion of the fluid and
has an impedance over at least a portion of its length to produce a
pressure drop in fluid therealong. This embodiment may additionally
be combined with an expansion device. On the other hand, the
conduit carrying fluid to the evaporator may perform none or little
expansion of the fluid and a separate expansion device may be
provided between the conduit and evaporator.
Advantageously, this arrangement provides a simple heat exchanger
for enabling heat to be exchanged between fluid flowing to and from
the evaporator of a refrigeration system.
According to another aspect of the present invention, there is
provided an apparatus for a refrigeration system comprising an
accumulator having a chamber for receiving refrigerant; an expander
for expanding refrigerant and disposed in said chamber, wherein
said expander comprises a conduit for carrying refrigerant
therethrough, said conduit having an impedance over at least a
portion of its length to produce a pressure drop in fluid
therealong, and wherein said conduit is arranged in said chamber
such that a major part of the surface area of the conduit in said
chamber is positioned for heat exchange with gaseous and/or
two-phase refrigerant.
In this arrangement, the conduit acts as an expansion device and at
the same time is arranged for heat exchange predominantly between
refrigerant flowing to the evaporator and gaseous or two-phase
refrigerant flowing from the evaporator to a compressor of a
refrigeration system. In this embodiment, the conduit may be
arranged such that a major part of the surface area of the conduit
is disposed in an upper portion of the chamber or above a level of
liquid refrigerant in the chamber so that heat exchange is
predominantly with gaseous and/or two-phase refrigerant.
In some embodiments, the apparatus further comprises an enclosure
in the chamber, the enclosure being defined by an enclosure wall
and having a fluid inlet and a fluid outlet, and wherein the major
surface of the conduit is in heat exchange relationship with the
interior of the enclosure.
In some embodiments, the expander conduit is disposed in the
enclosure.
In some embodiments, the enclosure comprises a conduit.
Advantageously, the conduit provides a means of directing fluid
from the evaporator along the expansion conduit so that the
resulting flow of fluid from the evaporator can continuously absorb
heat and possibly increase in temperature so that the fluid
entering the compressor is in a super heated rather than saturated
state.
According to another aspect of the present invention, there is
provided an apparatus for a refrigeration system comprising an
accumulator having a chamber for receiving refrigerant, and
expansion means for expanding refrigerant, the expansion means
comprising a conduit for carrying fluid therethrough and being
arranged for exchanging heat with refrigerant in said chamber, said
conduit having an impedance over at least a portion of its length
to produce a pressure drop in fluid therealong, said expansion
means further comprising means for defining one or more restrictive
orifice sized to increase the impedance of fluid flow above the
impedance provided by said conduit.
In this arrangement, the expander for expanding refrigerant
comprises a combination of a conduit having an impedance for
producing a pressure drop in fluid therealong and means defining
one or more restrictive orifices which also provide an impedance.
As the impedance is shared between an expansion conduit and an
orifice type expansion device, the impedance of the expansion
conduit may be reduced or relaxed as compared to an embodiment in
which the expansion device solely comprises an expansion conduit.
This allows the cross-sectional area, and therefore the surface
area of the expansion conduit to be increased, thereby increasing
the surface area over which heat exchange can take place for
increased efficiency.
In some embodiments, the apparatus further comprises valve means
for varying the size of at least one orifice.
According to another aspect of the present invention, there is
provided an apparatus for a refrigeration system comprising an
accumulator having a chamber for receiving refrigerant, an expander
for expanding refrigerant comprising a conduit for carrying fluid
therethrough, said conduit having an impedance over at least a
portion of its length to produce a pressure drop in fluid
therealong, and control means for controlling the impedance of the
expander.
In this arrangement, the expander comprises a conduit which
advantageously allows the expander to perform heat exchange as well
as expansion of refrigerant into an evaporator, and the control
means allows the impedance of the expander to be controlled,
thereby enabling the temperature of the refrigerant at the inlet of
the evaporator and the cooling capacity of the evaporator to be
controlled.
In some embodiments, the control means comprises valve means for
controlling the flow of fluid therethrough.
In some embodiments, the apparatus further comprises an enclosure
being defined by an enclosure wall and having a fluid inlet and a
fluid outlet, and wherein the expander conduit is disposed in the
enclosure. This arrangement allows heat exchange between liquid in
the accumulator and refrigerant in the expansion conduit to be
reduced and promotes heat exchange with gaseous and/or two-phase
refrigerant from the evaporator so that liquid in the refrigerant
flowing from the evaporator can be removed before the fluid enters
the compressor.
According to another aspect of the present invention, there is
provided a refrigeration system comprising an evaporator and a
compressor, a first conduit for feeding fluid compressed in the
compressor to the evaporator, and a second conduit for feeding
fluid from the evaporator to the compressor, wherein said first and
second conduits are in heat exchange relationship, and said first
conduit has an impedance along at least a portion of its length for
expanding said fluid as the fluid flows therealong towards said
evaporator.
According to another aspect of the present invention, there is
provided a refrigeration system comprising an evaporator and a
compressor, a first conduit for feeding fluid compressed in the
compressor to the evaporator and a second conduit for feeding fluid
from the evaporator to the compressor wherein the first and second
conduits are in heat exchange relationship and the system is
without an accumulator between the evaporator and compressor.
According to another aspect of the present invention, there is
provided an expansion device for a refrigeration system, the
expansion device having one or more restrictive orifices, valve
means for varying the size of at least one orifice, wherein the
valve means comprises an element capable of assuming a curve along
its length and wherein the tightness of an assumed curve is varied
by temperature such that the tightness of the curvature is varied
in a plane which extends across the orifice.
In some embodiments, the element comprises a first element
comprising a first material and a second element comprising a
second material, wherein the first material has a different
coefficient of thermal expansion than that of the second material,
and the elements are positioned side by side in the plane.
In some embodiments, the element comprises an elongate strip formed
as a spiral.
In some embodiments, the element is mounted such that the element
overlaps the orifice to vary the size of the orifice in response to
changes in temperature.
One embodiment of the present invention provides an integrated
accumulator-expander-heat exchanger. In some embodiments,
accumulators can be characterized as having three regions: a
gas-phase region, a liquid-phase region and a two-phase region.
From an energy utilization point of view, the expansion tube(s)
should be placed in the two-phase region and/or gas-phase region of
the accumulator-expander-heat exchanger, to heat the refrigerant to
a temperature close to or higher than the ambient so that the
irreversible loss of the system to the external environment
decreases and the larger specific cooling capacity will increase
the system COP. In embodiments of the present invention, the
expansion tube(s) can be immersed in liquid, but exchanging heat
with the two-phase and/or gas-phase fluid is preferred. A
superheated gas can then be supplied to the compressor.
In accordance with embodiments of the present invention, the high
temperature refrigerant from the high pressure side is sub-cooled
to lower temperatures on passage through the expansion conduit, and
the expansion conduit simultaneously effects expansion of the
refrigerant to a lower quality (liquid richer) state, compared with
conventional cycles for the introduction into the evaporator. In
addition, this brings vaporous refrigerant generated in the
evaporator or in the accumulator-expander-heat exchanger to a
higher quality or even a superheated gaseous state for return to
the compressor, which will increase the COP of compressor.
The refrigeration system is primarily for use in refrigerators,
freezers, air-conditioners, and heat pumps, particularly in
automotive air-conditioning systems, but may be used in any other
systems.
BRIEF DESCRIPTION OF THE DRAWINGS
Examples of embodiments of the present invention will now be
described with reference to the drawings, in which:
FIG. 1 is a schematic flow diagram of a conventional
air-conditioning system;
FIG. 2 is a schematic flow diagram of a known air-conditioning
system using an accumulator with internal heat exchanger;
FIG. 3 is a schematic flow diagram of an air-conditioning system
(which maybe used for cooling or for heating) using an integrated
accumulator-expander-heat exchanger of an embodiment of the present
invention;
FIG. 4 is a cross-sectional view of an integrated
accumulator-expander-heat exchanger of a first embodiment of the
present invention;
FIG. 5 is a cross-sectional view of an integrated
accumulator-expander-heat exchanger of a second embodiment of the
present invention;
FIG. 6 is a cross-sectional view of an integrated
accumulator-expander-heat exchanger of a third embodiment of the
present invention;
FIG. 7 is a cross-sectional view of an integrated
accumulator-expander-heat exchanger of a fourth embodiment of the
present invention;
FIG. 8A is a partial top view of a heat exchanger of an embodiment
of the present invention;
FIG. 8B is a partial cross-sectional view of a heat exchanger of
another embodiment of the present invention;
FIG. 9 shows a cross-sectional view of an integrated
accumulator-expander-heat exchanger according to another embodiment
of the present invention;
FIG. 10A shows a plan view of a valve according to an embodiment of
the present invention; and
FIG. 10B shows a cross-section of the valve shown in FIG. 10A along
the line A-A.
DESCRIPTION OF EMBODIMENTS
In a conventional air-conditioning system 5 of FIG. 1, liquid
refrigerant is stored in an accumulator 11 to be drawn in
gaseous-liquid two-phase form to the inlet of a compressor 12. The
compressor 12 delivers high temperature--high pressure refrigerant
gas (i.e. substantially higher than ambient) to a condenser/gas
cooler 14 where the gas is cooled and/or typically partially
converted to a liquid form. Refrigerant fluid from the condenser 14
(still under high pressure) is expanded to a lower pressure through
an expansion device 22, thereby undergoing a rapid drop in
temperature; the low temperature low pressure fluid is then
evaporated in an evaporator 18 from where it is returned to the
accumulator 11 in a mixed flow of liquid and gas. Depending upon
the loading of the system, more or less refrigerant fluid is
condensed and evaporated; refrigerant that is in excess of the
instantaneous requirements of the system is stored in liquid form
in the accumulator 11. The compressor, condenser, expansion device
and evaporator together with the conduits which interconnect these
components form a refrigerant loop for the refrigeration
system.
FIG. 2 shows a known air-conditioning system 3 using an accumulator
with internal heat exchanger 13, which modifies the conventional
system 5 of FIG. 1 by directing the partially cooled refrigerant
fluid delivered from the condenser 14 through a heat exchange coil
16 in the accumulator 13.
An air-conditioning system 1 of an embodiment of the present
invention shown in FIG. 3 generally comprises a conventional
refrigerant compressor 12, a condenser 14 and an evaporator 18
which are operatively coupled together by a conduit arrangement
which includes a length of capillary tube or conduit 20, disposed
between the condenser 14 and the evaporator 18, and housed within
an integral accumulator-expander-heat exchanger assembly 10.
The embodiment shown in FIG. 3 modifies the system of FIG. 2 by
using a capillary tube 20 placed within the accumulator 10 to
perform the functions of internal heat exchanger 16 and the
expansion device 22 shown in FIG. 2. As is more fully described
hereinafter, the capillary tube 20 is placed in an inner tube and
preferably not in contact with the refrigerant liquid in the
accumulator 10, but rather is positioned to be contacted by
refrigerant vaporous-liquid two phase and/or refrigerant gas that
is withdrawn from the accumulator 10 by the compressor 12. The
purpose of capillary tube 20 is to provide a heat transfer
interface to pre-cool the high pressure refrigerant and to ensure
complete vaporization of the refrigerant delivered to the
compressor 12.
The structure of an embodiment of the accumulator 10 is more
clearly shown in FIG. 4 and comprises a cylindrical container 24,
the upper end of which is attached and preferably hermetically
sealed to a disc-shaped head fitting 26. Other shapes of the
container 24 and the head fitting 26 and other sealing means are
contemplated by embodiments of the invention. The container 24 and
the head fitting 26 together define a chamber 27 which includes a
plurality of ports to receive the following connections: a low
pressure inlet port 28 to deliver refrigerant fluid from the
evaporator; a low pressure outlet port 30 through which refrigerant
gas is passed from the accumulator to the compressor 12; a high
pressure inlet port 32 and a low pressure (after expansion) outlet
port 34 communicating with the capillary tube 20 for delivering the
refrigerant fluid from the condenser/gas cooler 14 to the
evaporator 18. The low pressure inlet port 28, the low pressure
outlet port 30, the high pressure inlet port 32 and the high
pressure outlet port 34 on head fitting 26 may be placed in any
suitable arrangement or configuration depending on the space of
head fitting 26 and convenience of manufacture.
The container 24 preferably has a sump 50, which may be formed in a
central region of the bottom of the chamber 27. The sump 50
collects and stores oil, which is used to lubricate the compressor
and other components of the refrigeration system.
An enclosure, which in this embodiment has the form of a tube 36
with a vapor inlet end 38 and a low pressure outlet end 39 is
positioned inside the cylindrical container 24. In this embodiment,
the tube 36 is an aluminum cylindrical J-tube formed in two
longitudinal halves which are welded together after the capillary
tube 20 is inserted into the tube 36. However, the tube 36 may have
any other desirable shape, including linear, and may be formed from
any suitable materials such as stainless steel or copper, or a
polymeric material such as a plastic material. A short tube 40 is
connected (e.g. welded) to the outside of tube 36 surrounding the
low pressure outlet end 39 for welding two parts of tube 36
together after the capillary tube 20 is inserted into the tube 36.
The tube 36 extends generally vertically from the low pressure
outlet port 30 into the lower portion of the container 24 and is
curved in the region of its lowest point 42. The tube 36 extends
upwardly from the lowest point 42 to the inlet end 38. The tube 36
further preferably has one or more oil bleeding holes 44 in the
curved portion of the tube, which allow small amounts of oil to be
drawn out of the sump 50 and into the tube where the oil is mixed
with gaseous refrigerant.
A capillary tube 20, one end 29 of which is connected to the high
pressure inlet port 32 and the other end 31 of which is connected
to the high pressure outlet port 34, is positioned inside the
container 24. The capillary tube 20 enters the tube 36 adjacent the
low pressure outlet end 39 and exits the tube 36 adjacent the vapor
inlet end 38 such that substantially all of the capillary tube 20
is arranged inside the tube 36. This helps to ensure that the
capillary tube is in direct contact with the gasous/two-phase
refrigerant rather than the liquid refrigerant, and that the
refrigerant flows along the capillary tube over a substantial
portion of its length to promote efficient heat exchange. The tube
36 is preferably 50% immersed in liquid refrigerant, but this
amount may vary substantially, depending on such factors as the
heat load and operation of the system. Inside the tube 36 there is
gaseous refrigerant with a little liquid from the bleeding hole(s)
44.
The capillary tube 20 may have any desired cross sectional shapes,
such as circular, elliptic, rectangular or other forms. The
capillary tube 20 may be in any desired shape, such as the shape of
wave, helix and straight line, or any combination of them. The
capillary tube 20 may be formed from any suitable material
including but not limited to copper, stainless steel, or aluminum.
Preferably the capillary tube 20 is circular in cross sectional
shape, helix/wavy in shape and is formed of copper. The capillary
tube 20 may also be comprised of multiple tubes or coaxial tubes.
In one embodiment, a coaxial tube is formed by an internal tube and
external tube with internal ridges thereon. In another embodiment,
a coaxial tube is formed by an external tube and an internal tube
with external ridges thereon. The capillary tube 20 provides an
impedance to flow.
In operation, the accumulator 10 is placed into an air conditioning
or refrigeration system such as that shown in FIG. 3, in connection
with which the refrigerant flow scheme has already been discussed.
Therefore, only the flow passing through the accumulator 10 will
now be specifically described. The arrows in FIG. 4 illustrate the
flow of refrigerant through the accumulator 10 and the capillary
tube 20. From the condenser/gas cooler 14 (FIG. 3), the high
temperature liquid/vapor refrigerant flows into the accumulator 10
through the high pressure inlet port 32, and then into the
capillary tube 20 where it expands and rejects heat to the low
temperature refrigerant outside and is discharged at the outlet
port 34 into the evaporator 18 (FIG. 3). Simultaneously, the
primarily vaporous refrigerant exits the evaporator 18 and flows
into the low pressure inlet port 28 of the container 24. Liquid
refrigerant accumulates at the bottom of the container 24, and the
vaporous refrigerant, which is drawn by the compressor, rises and
enters the vapor inlet end 38 of the tube 36. The vaporous
refrigerant flows through the tube 36 and carries liquid
refrigerant and oil from the oil bleeding hole(s) 44 in the curved
portion of the tube 36 and then they mix into a two-phase flow. The
vaporous and two-phase refrigerant in the tube 36 absorb heat from
the high pressure (capillary tube) side, while high temperature
refrigerant is passing through the capillary tube 20. The low
pressure, low temperature two-phase fluid or superheated
refrigerant is then drawn out of the accumulator 10 through the low
pressure outlet port 30 and flows to the compressor 12 (FIG.
3).
The optimized effect for both expansion and heat exchange is
achieved by properly selecting the inner diameter and length of
capillary tube 20 and the size of conduit (typically 1/2-11/2
inches) connecting the evaporator to the compressor according to
certain working conditions, e.g. cooling capacity and working
temperature. The capillary tube 20 has a sufficiently small inner
diameter and sufficiently long length to effect sufficient
expansion of the high pressure refrigerant to low pressure to
obtain the required state of refrigerant at the inlet of the
evaporator 18, for example mostly liquid with little or no vapour
(i.e. a low quality state).
The capillary tube 20 may have an inner diameter in the range of
about 0.6 to 2.5 mm (0.025 to 0.100 inch) and a length in the range
of about 0.3 to 6 m (1 to 20 feet). For automobile systems the heat
transfer area of the capillary tube must be sufficient for system
requirements. When the length is relatively long, a compact
arrangement should be considered, such as coiled tubes.
The sub-cooling process of the refrigerant in the container 24 is
sufficient to provide the refrigerant in the capillary tube 20 with
a temperature at least 10 Celsius lower than the temperature of the
refrigerant at the outlet of the condenser/gas cooler 14. Depending
on the selection of capillary tube 20 in different situations, the
sub-cooled temperature of refrigerant changes accordingly and falls
into the range of about 10 to 25 Celsius when the discharge
temperature of the condenser/gas cooler 14 is about 10 to 20
Celsius above ambient temperature.
Advantageously, arranging the expansion tube 20 in an enclosure
such as the conduit 36 ensures that heat is predominantly exchanged
between refrigerant in the expansion tube and gaseous rather than
liquid refrigerant from the evaporator. Thus, in contrast to the
system disclosed in U.S. Pat. No. 5,622,055, the present system
does not rely on liquid refrigerant to cool the refrigerant in the
expansion tube, so that there is no demand on the present system to
produce additional amounts of liquid for this purpose. This allows
all of the liquid produced to be available to the evaporator for
cooling, thereby improving the cooling capacity of the system. This
is particularly beneficial in transcritical systems (e.g. which use
cool refrigerant), where liquefaction is more difficult to achieve
than in non-transcritical systems. Furthermore, as the present
system allows the refrigerant entering the compressor to be in a
superheated, rather than saturated state, the outlet temperature of
the compressor and therefore the temperature difference across the
cooler/condenser can be higher, resulting in a more efficient
refrigeration cycle.
Although FIG. 4 shows a favorable embodiment of the present
invention, in which all of the fluid connections extend through the
head fitting 26, other arrangements are possible, for example, as
shown in FIG. 5 where an accumulator 110 has a low pressure inlet
port 128, a high pressure inlet port 132 and a high pressure outlet
port 134 arranged in a head fitting 126. A low pressure outlet port
130 extends through a wall of a container 124.
A further possible embodiment is shown in FIG. 6. In FIG. 6, a
capillary 220 is positioned inside a tube 236 with both ends 221 of
the capillary positioned near a low pressure outlet port 230. The
capillary 220 also has a turn 246 near a vapor inlet end 238 of the
tube. Thus, in the capillary tube 220, refrigerant fluid flows in
opposite directions before and after the turn 246. In this
embodiment, the turn 246 may be positioned at any location inside
the tube 236. The capillary tube 220 may have more than one turn.
The capillary tube 220 may have any desired shape, such as the
shape of wave, helix and straight line, or any combination of them.
The capillary tube(s) 220 may have any of the features as described
with respect to capillary tube 20.
FIG. 7 shows still another possible embodiment. In this case, a
capillary 320 is positioned inside a tube 336 with both ends 321
near a vapor inlet end 338, and has a turn 346 near a low pressure
outlet port 330. Thus, in the capillary tube 320, refrigerant fluid
flows in opposite directions before and after the turn 346. As with
the embodiment of FIG. 6, in this embodiment, the turn 346 may be
positioned at any location inside the tube 336. The capillary may
have any number of turns, and any desired shape and/or other
features as described with respect to capillary tube 20.
The operation of accumulators 110, 210 and 310 of FIGS. 5 to 7 are
otherwise the same as the operation of the accumulator 10 described
in detail with respect to FIG. 4.
FIGS. 8A and 8B depict an embodiment of the invention in which
heat-transfer occurs outside an accumulator and an accumulator may
optionally not be used. The refrigerating system of FIG. 2 or 3 is
modified by removing the accumulator and instead placing the
conduit which extends between the condenser 14 and the expansion
device 22 and the conduit which extends between the evaporator 18
and the compressor 12 in heat transfer communication. In
particular, FIG. 8A depicts a conduit 420 which extends between the
condenser and the expansion device and a conduit 421 which extends
between the evaporator and the compressor. Preferably, these
conduits are comprised of metal (e.g. aluminum), although any
suitable material of any acceptable cross-sectional shape may be
used. These conduits are arranged in heat exchange relationship
with each other. This may be achieved by placing the conduits in
(intimate) contact with one another by, for example, welding,
soldering or otherwise joining the two conduits together. This
arrangement then takes the place of the tube 36 and capillary tube
20 depicted in FIGS. 4 through 7.
FIG. 8B shows another embodiment in which the arrangement of the
conduits are similar to those depicted in FIG. 4 but are again
independent of any accumulator. The inner conduit is a
capillary/small-sized tube 520 and the outer conduit is a tube. The
inner conduit may be sized to function as an expander (as for
example described above in connection with the capillary tube 20),
in which case a separate expansion device may be omitted.
Alternatively, the inner tube may be sized not to provide any
significant pressure drop in the refrigerant, in which case a
separate expansion device 22 is required.
Inputs and outputs 428 to 434 and 528 to 534 are as described in
respect to inputs and outputs 28 to 34 in regard to FIG. 4. Similar
arrangements of tubes may be provided as described in regard to
capillary tube 20. In operation, the fluid flowing from the
condenser to the evaporator and the fluid flowing from the
evaporator to the compressor undergo heat transfer when the
conduits carrying the fluid are in heat transfer contact as shown
in FIGS. 8A and 8B. The embodiments of FIGS. 8A and 8B are
particularly applicable to automotive air-conditioning systems.
In one embodiment, the heat exchange relationship between the
conduits may extend to a position close to or at the compressor
and/or the outlet of the cooler/condenser to assist in increasing
the heat transfer between the refrigerant paths.
FIG. 9 shows an accumulator according to another embodiment of the
present invention. The accumulator is similar to that described
above with reference to FIG. 4, and like parts are designated by
the same reference numerals. Thus, the description of the
accumulator shown in FIG. 4 applies equally to the accumulator
shown in FIG. 9. One of the main differences between the embodiment
of FIG. 9 and that shown in FIG. 4 is that the embodiment of FIG. 9
includes a valve 48 for controlling the flow of fluid into the
evaporator. The valve comprises one or more orifices whose size can
be varied to control the flow of fluid. The ability to adjust the
flow rate into the evaporator has important benefits in certain
applications, for example, where the compressor speed can vary.
Once such application is in automobiles where the compressor is
driven by the engine and therefore compressor speed is dependent on
the engine speed. When idling (i.e. the engine speed is low), the
flow of fluid through the refrigeration circuit decreases in
comparison with cruising speeds, and therefore the cooling capacity
of the refrigeration system is reduced. However, the heat load on
the system may be the same or may be even higher when a vehicle is
stationary. Advantageously, the provision of a variable valve
allows the impedance, and therefore, the pressure drop across the
expansion device to be increased to lower the temperature of
refrigerant entering the evaporator, thereby compensating for the
reduced fluid flow caused by slower compressor speeds.
Conveniently, the valve may be controlled in response to a
parameter indicative of the performance of the refrigeration
system, such as the temperature of the evaporator (or fluid
pressure). The valve may comprise a temperature sensitive actuator
which senses the local temperature at the port 28 and activates the
valve accordingly.
A valve according to an embodiment of the present invention is
shown in FIGS. 10A and 10B.
Referring to FIGS. 10A and 10B, a valve 60 comprises a support 50,
which in this embodiment comprises a cylindrical wall. The valve
further comprises a transverse portion 54 which extends across the
cylindrical support 50, and which in this embodiment is in the form
of a disc or plate. First and second orifices 56, 58 are formed in
the transverse portion 54 to allow fluid to pass therethrough. The
valve further comprises a valve element 60 mounted on the
transverse portion for controlling the amount by which the orifices
56, 58 are open or closed.
In this embodiment, the valve element 60 is in the form of an
elongate spiral strip and comprises two longitudinal elements 62,
64, one of which 62 is positioned on the outside of the spiral and
the other 64 is positioned on the inside of the spiral. In this
embodiment, the elements are arranged such that when the
temperature increases, the spiral element moves outwardly towards
the two orifices 56, 58 in the direction of arrows "b", and when
the temperature decreases, the spiral element moves inwardly away
from the orifices 56, 58, as indicated by arrows "c". To implement
this arrangement, the inner element 64 may comprise a material
having a lower coefficient of thermal expansion than the outer
element 62 so that when the temperature increases, the inner
element tends to reduce the tightness of curvature of the spiral so
that the valve element moves over the orifices 56, 58, and when the
temperature decreases, the inner element contracts more than the
outer element tending to increase the tightness of curvature of the
spiral, thereby moving the valve element away from the orifices and
towards the centre of the spiral. The valve element 60 may be
mounted so that its outer portions which control the orifice size
are free to slide relative to the transverse portion 54, and to
effect this, the spiral element may be fixedly mounted to the
transverse element in a central region thereof, for example region
66. Any suitable means of fastening the valve element to the
transverse portion 54 may be used, for example welding, solder,
adhesive or any suitable mechanical fastener such as a screw, rivet
or other mechanical device.
The inner and outer valve elements 62, 64 may comprise any suitable
material or may comprise any suitable structure which provides
differential expansion and contraction between the inner and outer
portions of the spiral strip. For example, the inner element 64 may
comprise copper, aluminum or other material, and the outer element
may comprise for example Invar.TM. or Kovar.TM., or other suitable
material.
Although the valve 48 may be mounted with the valve element on the
low pressure side of the orifice(s), it may be advantageous to
mount the valve element on the high pressure side, as shown in FIG.
10B, as the transverse portion 54 assists in supporting the valve
element 62 to minimize deflection thereof caused by flow and
pressure of fluid which have a direction indicated by arrow "d"
shown in FIG. 10B, and which act in the same direction as the
fastener for fastening the valve element to the transverse element
54.
It will be appreciated that in other embodiments, the valve may
comprise any number of orifices, for example, a single orifice or
more than two orifices. The orifices may have any desired
cross-sectional shape, such circular, triangular, quadrilateral, or
any combination of them. Although in this embodiment, the orifices
are placed adjacent the outer edge of the transverse element, in
other embodiments, one or more orifices may be positioned
elsewhere, for example, at any intermediate position between the
outer edge and centre of the transverse element. In another
embodiment, the spiral element may be adapted to contract when the
temperature increases and expand when the temperature decreases so
that it moves across the orifice in response to temperature changes
in the opposite manner described above.
Advantageously, the configuration of the valve according to the
above embodiments is compact and can be easily mounted into the
upper plate of the accumulator, as shown in FIG. 9. Furthermore,
this configuration allows the valve to be manufactured using very
few parts, and is therefore simple and cheap to manufacture and
also robust and reliable.
Although in some embodiments, an expansion valve such as one
described above in conjunction with FIGS. 9, 10A and 10B may be
positioned on the inlet side of the conduit 20, in other
embodiments, the expansion valve is placed on the outlet side of
the conduit 20, as shown in FIG. 9. In this way, the valve is
nearer to the evaporator and can sense temperature changes in the
evaporator directly without requiring any additional means of
conveying this control parameter to the expansion valve.
An expansion device comprising the combination of a restrictive
conduit (for example a capillary tube) and a restrictive orifice
causes the overall pressure drop across the expansion device to be
shared between these two elements, i.e. the conduit and orifice.
Advantageously, as the restrictive orifice produces its own
pressure drop, and therefore all of the pressure drop across the
expansion device is not attributed solely to the restrictive
conduit, the combination allows the restrictive conduit to have a
lower impedance than it would otherwise need. In turn, this allows
the internal cross-section of the restrictive conduit to be
enlarged, resulting in a larger circumference and conduit wall
surface area for increased heat exchange with fluid from the
evaporator. In this way, the synergy of the combination of a
restrictive conduit and a restrictive orifice provide an expansion
device having a higher efficiency. It is to be noted that the
benefits of this combination are achieved regardless of whether or
not a valve is provided for controlling the size of the restrictive
orifice, and embodiments may be implemented using the combination
of a restrictive conduit and simple restrictive orifice without any
valve element. Alternatively, or in addition, this combination
allows the length of the restrictive conduit to be reduced so that
it takes up less space.
It will be appreciated that while in FIG. 9, the enclosure 36 and
conduit 20 are positioned within the accumulator chamber, these
elements may be positioned outside the accumulator chamber, and may
or may not be arranged in such a way that the enclosure 36 is in
heat exchange relationship with fluid in the chamber.
Where in other embodiments, the enclosure 36 is omitted, the
restrictive conduit 20 may reside either within the accumulator
chamber or externally thereof and in heat exchange relationship
with fluid in the chamber, and in particular with the
gaseous/two-phase fluid.
Referring again to FIG. 9, in one optional implementation, the
conduit which carries refrigerant fluid from the cooler/condenser
14 to the accumulator is positioned in heat exchange relationship
with the conduit which carries fluid from the accumulator to the
compressor 12. Advantageously, this extends the heat exchange
relationship between the two fluid paths and promotes further
cooling of high pressure fluid between the condenser and the
accumulator, and further heating of low pressure fluid between the
accumulator and the compressor, for improved efficiency.
The tube 70 may be a capillary tube or an ordinary tube with no
significant impedance. The tubes/conduits 70, 72, may be arranged
in any way to effect heat exchange therebetween.
Experiments have shown that embodiments of the present system,
having an integrated accumulator-expander heat exchanger similar to
that shown in FIG. 4, and implemented as an air conditioning system
provide increased COP's of ca. 15%, and higher cooling loads of ca.
14% in comparison to another air conditioner using the same
compressor, evaporator, condenser, and the same capillary tube as
expansion device. Compressor speeds used in the experiments were
700, 1500 and 2000rpm, which generally correspond to idle, local
and highway driving, respectively.
Within the ambits of the invention significant changes can be made
in the dimensions, shapes, sizes, orientations and materials to
meet the specific requirements of the air-conditioning system that
is being designed. Likewise the external structure such as the head
fitting, the container, the position and arrangement of inlet and
outlet ports can be modified as desired.
It should be understood that while for clarity certain features of
the invention are described in the context of separate embodiments,
these features may also be provided in combination in a single
embodiment. Furthermore, various features of the invention that for
brevity are described in the context of a single embodiment may
also be provided separately or in any suitable sub-combination in
other embodiments.
Moreover, although particular embodiments of the invention have
been described and illustrated herein, it will be recognized that
modifications and variations may readily occur to those skilled in
the art, and consequently it is intended that the claims appended
hereto be interpreted to cover all such modifications and
equivalents.
* * * * *